chore: complete v1.1 milestone

Archive v1.1 Calendar & Polish milestone artifacts (roadmap,
requirements, phase directories) to milestones/. Evolve PROJECT.md
with validated requirements and new key decisions. Update
RETROSPECTIVE.md with v1.1 section and cross-milestone trends.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.planning/config.json

@@ -5,7 +5,7 @@
   "commit_docs": true,
   "model_profile": "balanced",
   "workflow": {
-    "research": true,
+    "research": false,
     "plan_check": true,
     "verifier": true,
     "nyquist_validation": true,